Making a lube oil by hydrocracking and solvent extraction



United States Patent O 3,546,098 MAKING A LUBE OIL BY HYDROCRACKING ANDSOLVENT EXTRACTION Byron G. Spars, Mill Valley,'Calif., assiguor toChevron Research Company, San Francisco, Calif., a corporation ofDelaware No Drawing. Filed July 24, 1968, Ser. No. 747,101

Int. Cl. Cq 37/00 U.S. Cl. 208-96 11 Claims ABSTRACT OF THE DISCLOSURE Aprocess for the production of lubricating oil which is stable inultraviolet light, which comprises hydrocracking a heavy oil underspecified conditions to produce a lubricating oil fraction and thentreating the fraction with anhydrous or aqueous N,N-dimethylformamide ordimethylsulfoxide to produce an ultraviolet-light-stable lubricatingoil. Treating conditions are specified. High yields of stable oil areobtained.

BACKGROUND OF THE INVENTION This invention relates to processes for theproduction of lubricating oils. More particularly, it relates toprocesses for the production of stable lubricating oils by hydrocrackingand treating with selective extractants.

Lubricating oils, which can be defined in general as those hydrocarbonmaterials which boil above 600 F., are presently produced by twoprincipal methods. The first, which produces straight-run lubricatingoils, may include steps of distillation of a crude oil, solventrefining, solvent dewaxing, acid treating and clay contacting. Solventrefining is generally employed to separate the lubricating oilcomponents from the other components of the distilled oil.

The second method is somewhat similar to the first but substitutes mildhydrofining or hydrofinishing for one or more of the steps of solventrefining, acid treating or clay contacting. Hydrofining orhydrofinishing is a process wherein the contaminants in the crudedistillate are converted, by contacting with hydrogen in the presence ofa hydrogenating catalyst, to easily removable or harmless species. Onlyminimal cracking occurs during hydrofining.

Recently it has been discovered that lubricating oils may also beproduced by hydrocracking. In this process, a heavy petroleum oil iscontacted with hydrogen at elevated temperature and pressure in thepresence of a hydrocracking catalyst; and the hydrocracked product(which is often termed the hydrocrackate) is separated, usually bydistillation, into materials boiling in different temperature ranges.One or more of these materials will boil within the lubricating oilboiling range.

It has now been found that lubricating oils produced by hydrocracking,although having many desirable properties not otherwise obtainable bystraight-run processing, also possess to a significant degree oneundesirable property which had previously been noted only to aninsignificant degree with straight-run lube oils. This undesirableproperty is the instability of hydrocracked oils when exposed toultraviolet light in the presence of air. This instability is evidencedby the formation of a precipitate in the oil after a short period ofexposure to ultraviolet light. Such a precipitate is undesirable, notonly because it may prove detrimental to the lubrication function whichthe oil is designed to perform, particularly in high-performance oilssuch as turbine oils, but also because it reduces the esthetic value ofwhat would otherwise be a clear, premium-quality oil. The latter is nota trivial consideration; refiners have learned through experience thatconsumers will not buy lubricating oils which contain visibleprecipitates even though those precipitates might have no adverse effecton the performance qualities of the lubricating oil.

In the past, it has been known that certain types of lubricating oilinstability, such as oxidation instability, could be prevented bytreating the oil with any of a number of polar solvents, such as phenol,furfural and sulfuric acid. The acid treating of straight-run oilsreferred to above is such a treating process. While this treatment tendsto remove the ultraviolet instability-causing components, it isunselective, i.e., it has the disadvantage that it also removes aconsiderable portion of the desirable lubricating oil components alongwith the undesirable components. Such indiscriminate removal occurs byeither or both solvent extraction or chemical reaction with certaincomponents of the oil (e.g., when sulfuric acid treating results insulfonation of some oil components). Until now, it has been believedthat treatment of any oil with any of the polar solvents producedapproximately equivalent results; i.e., low yield of a moderately stableoil. Further, since ultraviolet instability was an insignificant problemwith straight-run oils, solvent treating was only sparingly used inorder to avoid the problem of resulting low yields. Such a solution isnot satisfactory, however, for hydrocracked oils where the problem ofultraviolet instability is a very significant one.

It has been known for some time that N,N-dimethy1- formamide(hereinafter referred to as DMF) and dimethylsulfoxide (hereinafterreferred to as DMSO) were useful as extractives to remove aromaticcompounds from mixtures of aromatics and paraflins. This extraactiveability has heretofore been believed to be restricted to the ability tomake only gross discriminations between aromatics and parafiins.Consequently, since it is thought that ultraviolet light instability isdue to the presence in the oil of only certain species of aromatics, ithas been believed that DMF and DMSO suffer from the same disadvantage asthe other polar solvents mentioned above.

SUMMARY OF THE INVENTION I have now unexpectedly discovered that underthe conditions found in the process of this invention DMF and DMSOexhibit selective extractive ability and remove essentially all theinstability-causing compounds, leaving a high yield of ultraviolet lightstable oil. Broadly stated, this invention comprises contacting in ahydrocracking zone a liquid hydrocarbon feedstock containing asubstantial portion of components boiling above 750 F. with hydrogen inthe presence of a hydrocracking catalyst at an elevated temperature andpressure in order to convert at least 15 weight percent of saidfeedstock components boiling above 750 F. to materials boiling below 750F., recovering from the effluent of said hydrocracking zone alubricating oil fraction boiling above 600 F., contacting saidlubricating oil fraction in contacting apparatus with a treating agentcomprising a selective ex tractant selected from the group consisting ofN,N-dimethylformamide, dimethylsulfoxide, aqueous solutions ofN,N-dimethylformamide, and aqueous solutions of dirnethylsulfoxide, andrecovering from the effiuent of said contacting apparatus a lubricatingoil with an improved ultraviolet light stability. 7

Treating is conducted at temperatures of 0250 F, and pressures of aboutatmospheric up to about 10 atmospheres. Room temperature and pressure ofabout 0-100 p.s.i.g. are preferred. Treating may be single stage ormultistage. Solvent-to-oil ratios are 0.255.0 volumes of solvent pervolume of feed. Use of this treating step allows production of highlystable oil in yields of or greater.

3 DETAILED DESCRIPTION OF THE INVENTION The process of this invention isa process for producing hydrocracked lube oils which are stable in thepresence of ultraviolet light. Any hydrocarbon oil having a substantialportion boiling above 750 F. may be hydrocracked in this process andconverted to lubricating oil. Preferred feeds are lubricating oil stocksboiling above 900 F., although crude oils, reduced crudes, residualoils, deasphalted oils, and the like, may also be used.

The hydrocracking step in this process is operated at a pressure in therange of from about 500 to about 5,000 p.s.i.g., a temperature in therange of 720850 F., a liquid hourly space velocity (LHSV) in the rangeof from about 0.2 to about 10.0 and a hydrogen throughput rate in therange of from about 1,000 to about 20,000 s.c.f./ bbl. More preferredconditions, which produce a higher yield of lubricating oils, are apressure of l,5003,000 p.s.i.g., a temperature of 750-830 R, an LHSV of0.5 2.0 and a hydrogen throughput rate of 5,000-l0,000 s.c.f./bbl. I

A critical element in the invention is the conversion of at least weightpercent of the materials boiling above 750 F. to materials boiling below750 F. by hydrocracking at elevated temperatures in the range of 720-850F., and preferably 750-830 F. If the temperature is below 750 F., theeffect of DMF and DMSO treating is lessened. This is believed due to thenature of the instability-causing components which appear to be certainpolynuclear aromatic compounds. At the lower temperatures, one or morerings of each of the polynuclear aromatic molecules will becomesaturated; and it is believed that in this partially or fully saturatedform the compounds are less susceptible to extraction by DMF and DMSO.Conversely, if the temperature of conversion is above 850 F., catalytichydrocracking is minimized and the predominant reaction is thermalcracking. The actual operating temperature will depend on the type offeed processed and its viscosity index, the viscosity index of thelubricating oil product desired, and the degree of conversion requiredto produce the desired viscosity index increase. It is usually foundthat feedstocks which contain higher proportions of aromatics requirehigher degrees of conversion which may be accomplished by hydrocrackingat a high temperature, low space velocity, or any combination ofrelatively more severe conditions within the acceptable ranges describedabove.

Hydrocracking may be accomplished in a single hydrocracking reactor,particularly when the feed to be treated requires only a small amount ofconversion to produce a lube oil suitable for DMF and DMSO treating.However, many of the common high boiling oil feeds require a largeamount of hydrocracking to produce acceptable lube oils. Consequently,when a high degree of conversion (e.g., more than 60 percent) isdesired, it is preferred to use two or more hydrocracking reactors inseries. This permits the hydrocracking process to be operated withconsiderable flexibility, for each reactor can be operated at somewhatbelow its maximum conversion potential, thus avoiding severe conditionsof temperature, pressure and space velocity which put an unnecessarystrain on the process equipment and shorten the useful life of thehydrocracking catalyst.

The catalyst used in the hydrocracking reactors may be of the sulfactivehydrogenation type commonly used for desulfurization anddenitrification. Suitable catalysts include combinations of the Group VIand Group VIII metals, oxides or sulfides associated with porousrefractory oxide carriers. The most suitable metal are nickel or cobaltin combination with molybdenum or tungsten as sulfides. The refractoryoxide may be alumina; but usually, to provide more hydrocrackingactivity, there is employed a combination of alumina with silica,magnesia, titania and other like materials or combinations of such otheroxides-for example, silica-magnesia. Such catalysts can be prepared in anumber of ways, including preparing the porous carrier first and thenimpregnating it with solutions of the metal compounds which are laterconverted to metal oxides by calcining. Particularly good catalysts foruse in the hydrocracking step can be prepared by coprecipitation orcogelation techniques wherein all of the components are initiallysupplied as dissolved compounds in aqueous solutions and coprecipitatedtogether. Zeolitic-supported hydrocracking catalysts may also be used.

As noted earlier, ultraviolet light instability is evidenced by theformation of a visible precipitate in the oil. The degree of stabilitypossessed is determined by the relative amount of time required for theprecipitate to form. One obvious way to measure this degree of stabilityis to expose the oil to the ultraviolet light in sunlight and observethe number of days required for the precipitate to form. This, however,is an unsatisfactory procedure for two related reasons; First, naturalultraviolet light is not concentrated, so the oils usually requireseveral weeks or months of exposure before any precipitate forms.Secondly, over this period of time, the daily exposure is not uniform,for the daily amount of sunlight varies with the time of year and theweather on any particular day. Consequently, in order to measureultraviolet stability rapidly and reliably, the following test has beendeveloped: A 5 ml. sample of the oil in a clear glass container isexposed to a 450 watt mercury vapor ultraviolet light (type L) placed ina closed cabinet with the oil sample and with a distance of 2 inchesbetween the oil sample and the light source. Light neutral oils whichform a precipitate in less than four hours exposure are considered to betoo unstable to be commercially acceptable. Oils which form precipitatesin more than four but less than ten hours are considered reasonablystable and marginally acceptable, although inferior, while those whichrequire more than ten hours exposure before precipitation are consideredof premium quality.

The contacting of the oil and treating agent occurs in what, forconvenience, will herein be termed the stabilization step. Thestabilization step, as defined in this process, may be a singlecontacting step or a plurality of contacting steps in series. Ingeneral, the single step procedure is preferred. The treating agent, asdefined in the claims, comprises an extractive selected from the groupconsisting of N,N-dimethylformamide, dimethylsulfoxide, aqueoussolutions of N,N-dimethylformamide, and aqueous solutions ofdimethylsulfoxide. It is preferred that if aqueous solutions are usedthe concentration of the DMF or DMSO in the solution not be less than 70volume percent, and a volume percent minimum is more preferred. Thepresence of water improves the yield of product oil, but at higheramounts of water the selectivity of the aqueous solution for extractionof the instability-causing components is decreased. If desired, smallamounts of other materials may be present during contacting if they arerestricted to minor portions and do not adversely affect the extractivepower of the chosen extractant.

Any conventional liquid-liquid contacting apparatus is suitable for usein this process if it provides for substantially complete contacting ofthe oil and the treating agent. Satisfactory methods of providingadequate contacting are well known in the art. The contacting apparatusused in the stabilization step should be operated at a temperature inthe range of from about 0 F. to about 250 F. It is most convenient tooperate in the range of 60-l50 F. Pressure must be sufficiently high tomaintain substantially all of each component in the liquid phase. Inmany cases, atmospheric pressure will be sufiicient to accomplish thisobjective. The suitable operating pressure range is from aboutatmospheric pressure to about 30 atmospheres gauge pressure. The mostconvenient operating pressures are those in the range of 0-300 p.s.i.g.The ratio of solvent to oil is 0.255.0 volumes of solvent per volume ofoil. It is most convenient to use ratios of 0.5-2.0 volumes of solventper volume of oil. Where the oil is relatively heavy and viscous, it isdesirable to add a hydrocarbon diluent to thin the oil and improve thedegree of contacting. Suitable diluents are the C -C paraflins,particularly butane or pentane. Of these two, butane is preferred,because it is more easily separated from the treated oil and recovered.Further, excess butane is more often available in oil refineries than isexcess pentane. Use of this diluent should not be confused with theprovision stated above that minor portions of other materials may bepresent in the treating agent. The diluent is an essentially inertmaterial used only to reduce the viscosity of the oil to be stabilizedand it may be present in any amount required to provide adequateviscosity reduction.

As stated above, it is known in the prior art that DMF and DMSO can beused as aromatic extractives. Thus they can be used to extract'thearomatics from oils boiling over a wide boiling range and not merelyrestricted to those produced byhydrocracking under the conditions statedin this process. However, the extractive power of DMF and DMSO underconditions other than those described in the process of this inventionis not selective for particular aromatics; and thus a substantialportion of the aromatic content of an oil will be removed by DMF or DMSOtreatment under those conditions. In most cases this will result in astable oil because the instability-causing aromatic compounds will havebeen removed. However, the yield of stable oil will be unnecessarily lowbe cause many additional aromatic compounds which play no part in theultraviolet light instability problem will also have been removed. Thestabilization process may be considered satisfactory only when oil yieldis at least 95 percent of feed and stability of the oil product is atleast 10 hours. The following Table I illustrates that under theconditions required in the process of this invention only DMF and DMSOprovide this degree of stability and yield while other extractants failto provide either or both a high yield of oil or a sufficiently stableoil. Data for this table were derived from experiments in which ahydrocracked oil was solvent treated at room temperature and atmosphericpressure with the volume of treating agent shown, and then subjected toultraviolent light in the standard test described above.

It is apparent from the above Table I that if treating agents other thanDMF and DMSO are used, yield must be sacrificed if a stable product isto be obtained, or, conversely, a high yield can be obtained only byaccepting an unstable and inferior product. Only DMF and DMSO' producestable products in high yield.

Typical results of treating hydrocracked lubricating oil stocks with DMFand DMSO, pure and in aqueous solution, are illustrated in the followingTable II. In each of the runs shown, the oil treated was a 700-1050 F.lubricating oil which had been produced by catalytically hydrocrackinghigh boiling gas oil to 65 percent conversion at about 780 F. and 2700p.s.i.g. The oil was mixed with one volume of pentane diluent and 1.4volumes of treating agent at room temperature and atmospheric pressure.

These data clearly illustrate that a high yield of high quality oil isobtained from the process of this invention.

A small amount of DMF or DMSO may remain in the treated oil followingthe contacting and subsequent separation of the oil and treating agent.This is not harmful to the oil as long as the residue of DMF or DMSO isnot too high. For instance, an oil with 100 p.p.m. residual DMF had 10hours of ultraviolet light stability prior to precipitation, while onewith 500 p.p.m. had 12 hours stability.

When the hydrocracked oil contains waxy components, these may be removedby conventional dewaxing procedures, such as solvent dewaxing. Dewaxingmay occur before or after the stabilization step described in thisspecification.

The preceding examples and descriptions are given for illustrativepurposes only. It is apparent that there are many embodiments of theprocess of this invention, and it is not intended that it be limitedother than as described in the appended claims.

I claim:

1. A process for the production of a high yield of lubricating oil whichis stable in the presence of ultraviolet light, which comprises:

(A) In a hydrocracking zone contacting a liquid hydrocarbon feedstockcontaining a substantial portion of components boiling above 750 F. withhydrogen in the presence of a hydrocracking catalyst at an elevatedtemperature and pressure in order to convert at least 15 weight percentof said feedstock components boiling about 750 F. to materials boilingbelow 750 F.;

(B) recovering from the effluent of said hydrocracking zone alubricating oil fraction boiling above 600 F.;

(C) contacting said lubricating oil fraction in contacting apparatuswith a treating agent comprising a selective extractant selected fromthe group consisting of N,N-dimethylformamide, aqueous solutions ofN,N-dimethylformamide, and aqueous solutions of dimethylsulfoxide; and

(D) recovering from the efliuent of said contacting apparatus alubricating oil with improved ultraviolet light stability.

2. The process of claim 1 wherein said improved stability of said oil issuch that no visible precipitate forms n the oil during 10 hoursexposure of the oil in an ultraviolet light test.

3. The process of claim 2 wherein said treating agent consistsessentially of a selective extractant selected from the group consistingof N,N-dirnethylformamide, aqueous solutions of N,N-dimethylformamide,and aqueous solutions of dimethylsulfoxide.

4. The process of claim 3 wherein said aqueous solutions ofN,N-dimethylformamide and dimethylsulfoxide contain at least 70 volumepercent of N,N-dimethylforn'tamide and dimethylsulfoxide, respectively.

5. The process of claim 3 wherein said aqueous solutions ofN,N-dimethylformamide and dimethylsulfoxide contain at least volumepercent of N,N-dimethylformamide and dimethylsulfoxide, respectively.

6. The process of claim 2 wherein the ratio of said treating agent tosaid lubricating oil fraction is 0.255.0.

7. The process of claim 2 wherein said contacting apparatus is operatedat a temperature in the range of 250 F. and a pressure of 0-300 p.s.i.g.

8. in a process for the production of a high yield of lubricating oil,which is stable in the presence of ultraviolet light, by contacting in ahydrocracking zone a liquid hydrocarbon feedstock containing asubstantial portion of components boiling above 750 F. with hydrogen inthe presence of a hydrocracking catalyst at an elevated temperature andpressure in order to convert at least 15 weight percent of saidfeedstock components boil ing above 750 F. to materials boiling below750 F., and recovering from the efiluent of said hydrocracking zone alubricating oil fraction boiling above 600 F.; the improvement whichcomprises:

contacting said lubricating oil fraction in contacting apparatus with atreating agent comprising a selective extractant selected from the groupconsisting of N,N-dimethylformamide, aqueous solutions of N,N-dimethylformamide, and aqueous solutions of dimethylsulfoxide, andrecovering from the efiiuent of said contacting apparatus a lubricatingoil with improved ultraviolet light stability.

9. A process for the production of a high yield of lubricating oil withan ultraviolet light stability of at least 10 hours, which compriseshydrocracking in a hydrocracking zone at elevated temperature andpressure, in the presence of hydrogen and a hydrocracking catalyst, ahydrocarbon feedstock containing a substantial portion of materialsboiling above 750 F., at a conversion of at least 15 weight percent ofsaid materials boiling above 750 F. to materials boiling below 750 F.,recovering from the efiiuent from said hydrocracking zone a lubricatingoil fraction boiling above 600 F., contacting said lubricating oilfraction in contacting apparatus with a treating agent comprisingdimethylsulfoxide, and recovering from said contacting apparatus alubricating oil product in a yield of at least weight percent, based onsaid lubricating oil fraction, said lubricating oil product having anultraviolet light stability of at least 10 hours.

10. A process as in claim 9, wherein said treating agent comprisingdimethylsulfoxide is dimethylsulfoxide.

11. A process as in claim 9, wherein said treating agent comprisingdimethylsulfoxide is an aqueous solution of dimethylsulfoxide.

References Cited UNITED STATES PATENTS 2,615,057 10/1952 Wolff et al.208322 3,005,032 10/1961 Makin 208322 3,077,733 2/1963 Axe et al 208963,308,055 3/1967 Kozlowski 20818 3,414,506 12/1968 Campagne 20818HERBERT LEVINE, Primary Examiner US. Cl. X.R.

PO-IWJ UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,5 46 ,098 Dated December 8 1970 Inventor(s) BYRON G. SPARS It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col 6 5th line of Table II a DMF (aqueous)" should ree ---95% DH?(aque0us)- Col 6 6th line of Table II "0% DMF (aqueous)" should rea--90% DMF (aqueous)- Signed and sealed this 20th day of July 1971 (SEAL)Attest:

EDWARD M.FLETCHER,J'R. WILLIAM E. SCHUYLER,

Attesting Officer Commissioner of Pate:

